DP Chemistry (first assessment 2025)
Question 22M.2.HL.TZ2.7a(iii)
| Date | May 2022 | Marks available | [Maximum mark: 1] | Reference code | 22M.2.HL.TZ2.7a(iii) |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Justify | Question number | a(iii) | Adapted from | N/A |
a(iii).
[Maximum mark: 1]
22M.2.HL.TZ2.7a(iii)
(a(iii))
Justify whether a 1.0 dm3 solution made from 0.10 mol NH3 and 0.20 mol HCl will form a buffer solution.
[1]
Markscheme
no AND is not a weak acid conjugate base system
OR
no AND weak base «totally» neutralized/ weak base is not in excess
OR
no AND will not neutralize small amount of acid ✔
Accept “no AND contains 0.10 mol NH4Cl + 0.10 mol HCl”.
Examiners report
Poorly answered revealing little understanding of buffering mechanisms, which is admittedly a difficult topic.
Syllabus sections
Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.1—Proton transfer reactions » Reactivity 3.1.17—The pH of a buffer solution depends on both: • the pKa or pKb of its acid or base • the ratio of the concentration of acid or base to the concentration of the conjugate base or acid. Solve problems involving the composition and pH of a buffer solution, using the equilibrium constant.